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From: Daniel Borkmann <daniel@iogearbox.net>
To: Brendan Jackman <jackmanb@google.com>, bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Florent Revest <revest@chromium.org>,
	Ilya Leoshkevich <iii@linux.ibm.com>
Subject: Re: [PATCH v2 bpf-next] bpf: x86: Fix BPF_FETCH atomic and/or/xor with r0 as src
Date: Wed, 17 Feb 2021 23:27:32 +0100	[thread overview]
Message-ID: <d7befe74-f340-2b3d-1ea4-05cc21b8dc4e@iogearbox.net> (raw)
In-Reply-To: <20210216125307.1406237-1-jackmanb@google.com>

On 2/16/21 1:53 PM, Brendan Jackman wrote:
> This code generates a CMPXCHG loop in order to implement atomic_fetch
> bitwise operations. Because CMPXCHG is hard-coded to use rax (which
> holds the BPF r0 value), it saves the _real_ r0 value into the
> internal "ax" temporary register and restores it once the loop is
> complete.
> 
> In the middle of the loop, the actual bitwise operation is performed
> using src_reg. The bug occurs when src_reg is r0: as described above,
> r0 has been clobbered and the real r0 value is in the ax register.
> 
> Therefore, perform this operation on the ax register instead, when
> src_reg is r0.
> 
> Fixes: 981f94c3e921 ("bpf: Add bitwise atomic instructions")
> Signed-off-by: Brendan Jackman <jackmanb@google.com>

Applied, thanks!

      parent reply	other threads:[~2021-02-17 22:28 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-16 12:53 [PATCH v2 bpf-next] bpf: x86: Fix BPF_FETCH atomic and/or/xor with r0 as src Brendan Jackman
2021-02-16 16:32 ` KP Singh
2021-02-17 22:27 ` Daniel Borkmann [this message]

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